Method of forming fine patterns

ABSTRACT

It is disclosed a method of forming fine patterns comprising: covering a substrate having photoresist patterns with an over-coating agent for forming fine patterns, applying heat treatment to cause thermal shrinkage of the over-coating agent so that the spacing between adjacent photoresist patterns is lessened by the resulting thermal shrinking action, and removing the over-coating agent substantially completely by way of bringing thusly treated substrate into contact with a remover solution for over 60 seconds.

This is a continuation of Ser. No. 10/681,145, filed Oct. 9, 2003, nowabandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method of forming fine patterns in the fieldof photolithographic technology. More particularly, the inventionrelates to a method of forming or defining fine patterns, such as holepatterns and trench patterns, that can meet today's requirements forhigher packing densities and smaller sizes of semiconductor devices.

2. Description of the Related Art

In the manufacture of electronic components such as semiconductordevices and liquid-crystal devices, there is employed thephotolithographic technology which, in order to perform a treatment suchas etching on the substrate, first forms a film (photoresist layer) overthe substrate using a so-called radiation-sensitive photoresist which issensitive to activating radiations, then performs exposure of the filmby selective illumination with an activating radiation, performsdevelopment to dissolve away the photoresist layer selectively to forman image pattern (photoresist pattern), and forms a variety of patternsincluding contact providing patterns such as a hole pattern and a trenchpattern using the photoresist pattern as a protective layer (maskpattern).

With the recent increase in the need for higher packing densities andsmaller sizes of semiconductor devices, increasing efforts are beingmade to form sufficiently fine-line patterns and submicron-electronicfabrication capable of forming patterns with linewidths of no more than0.20 μm is currently required. As for the activating light raysnecessary in the formation of mask patterns, short-wavelength radiationssuch as KrF, ArF and F₂ excimer laser beams and electron beams areemployed. Further, active R&D efforts are being made to find photoresistmaterials as mask pattern formers that have physical properties adaptedto those short-wavelength radiations. In addition to those approachesfor realizing submicron-electronic fabrication which are based onphotoresist materials, active R&D efforts are also being made on thebasis of pattern forming method with a view to finding a technology thatcan provide higher resolutions than those possessed by photoresistmaterials.

For example, JP-5-166717A discloses a method of forming fine patternswhich comprises the steps of defining patterns (=photoresist-uncoveredpatterns) into a pattern-forming resist on a substrate, then coatingover entirely the substrate with a mixing generating resist that is tobe mixed with said pattern-forming resist, baking the assembly to form amixing layer on both sidewalls and the top of the pattern-formingresist, and removing the non-mixing portions of said mixing generatingresist such that the feature size of the photoresist-uncovered patternis reduced by an amount comparable to the dimension of said mixinglayer. JP-5-241348 discloses a pattern forming method comprising thesteps of depositing a resin, which becomes insoluble in the presence ofan acid, on a substrate having formed thereon a resist patterncontaining an acid generator, heat treating the assembly so that theacid is diffused from the resist pattern into said resin insoluble inthe presence of an acid to form a given thickness of insolubilizedportion of the resist near the interface between the resin and theresist pattern, and developing the resist to remove the resin portionthrough which no acid has been diffused, thereby ensuring that thefeature size of the pattern is reduced by an amount comparable to thedimension of said given thickness.

However, in these methods, it is difficult to control the thickness oflayers to be formed on the sidewalls of resist patterns. In addition,the in-plane heat dependency of wafers is as great as ten-odd nanometersper degree Celsius, so it is extremely difficult to keep the in-planeuniformity of wafers by means of the heater employed in currentfabrication of semiconductor devices and this leads to the problem ofoccurrence of significant variations in pattern dimensions.

Another approach known to be capable of reducing pattern dimensions isby fluidizing resist patterns through heat treatment and the like. Forexample, JP-1-307228A discloses a method comprising the steps of forminga resist pattern on a substrate and applying heat treatment to deformthe cross-sectional shape of the resist pattern, thereby defining a finepattern. In addition, JP-4-364021A discloses a method comprising thesteps of forming a resist pattern and heating it to fluidize the resistpattern, thereby changing the dimensions of its resist pattern to formor define a fine-line pattern.

In these methods, the wafer's in-plane heat dependency is only a fewnanometers per degree Celsius and is not very problematic. On the otherhand, it is difficult to control the resist deformation and fluidizingon account of heat treatment, so it is not easy to provide a uniformresist pattern in a wafer's plane.

An evolved version of those methods is disclosed in JP-7-45510A and itcomprises the steps of forming a resist pattern on a substrate, forminga stopper resin on the substrate to prevent excessive thermal fluidizingof the resist pattern, then applying heat treatment to fluidize theresist so as to change the dimensions of its pattern, and thereafterremoving the stopper resin to form or define a fine-line pattern. As thestopper resin, a water-soluble resin, specifically, polyvinyl alcohol isemployed singly. However, the use of polyvinyl alcohol singly is nothighly soluble in water and cannot be readily removed completely bywashing with water, introducing difficulty in forming a pattern of goodprofile. The pattern formed is not completely satisfactory in terms ofstability over time. In addition, polyvinyl alcohol cannot be appliedefficiently by coating. Because of these and other problems, the methoddisclosed in JP-7-45510 has yet to be adopted commercially.

In addition, in forming patterns by utilizing photolithographytechniques, it is required the prevention of the occurrence of defectson the substrate and the improvement of throughput.

JP 2001-281886A discloses a method comprising the steps of covering asurface of a resist pattern with an acidic film made of a resist patternsize reducing material containing a water-soluble resin, rendering thesurface layer of the resist pattern alkali-soluble, then removing saidsurface layer and the acidic film with an alkaline solution to reducethe feature size of the resist pattern. JP-2002-184673A discloses amethod comprising the steps of forming a resist pattern on a substrate,then forming a film containing a water-soluble film forming component onsaid resist pattern, heat treating said resist pattern and film, andimmersing the assembly in an aqueous solution of tetramethylammoniumhydroxide, thereby forming a fine-line resist pattern without involvinga dry etching step. However, both methods are simply directed toreducing the size of resist trace patterns themselves and therefore aretotally different from the present invention in object. Further, thosepublications do not describe or suggest the effects of reducing theoccurrence of defects by way of adjusting the times of removing step bywashing with water.

SUMMARY OF THE INVENTION

The present invention has been accomplished under these circumstancesand has as an object providing a method of forming fine patterns on asubstrate having photoresist patterns (mask patterns) as it is coveredwith an over-coating agent. The method has high ability to reduce theoccurrence of defects and to improve throughput.

In order to attain this object, the present invention provides a methodof forming fine patterns comprising: covering a substrate havingphotoresist patterns with an over-coating agent for forming finepatterns, applying heat treatment to cause thermal shrinkage of theover-coating agent so that the spacing between adjacent photoresistpatterns is lessened by the resulting thermal shrinking action, andremoving the over-coating agent substantially completely by way ofbringing thusly treated substrate into contact with a remover solutionfor over 60 seconds.

In a preferred embodiment, the heat treatment is performed at atemperature that does not cause thermal fluidizing of the photoresistpatterns on the substrate.

DETAILED DESCRIPTION OF THE INVENTION

The method of preparing the substrate used in the pre-sent inventionhaving photoresist patterns thereon is not limited to any particulartype and it can be prepared by conventional methods employed in thefabrication of semiconductor devices, liquid-crystal display devices,magnetic heads and microlens arrays. In an exemplary method, aphotoresist composition of chemically amplifiable or other type is spin-or otherwise coated on a substrate such as a silicon wafer and dried toform a photoresist layer, which is illuminated with an activatingradiation such as ultraviolet, deep-ultraviolet or excimer laser lightthrough a desired mask pattern using a reduction-projection exposuresystem or subjected to electron beam photolithography, then heated anddeveloped with a developer such as an alkaline aqueous solution,typically a 1-10 mass % tetramethylammonium hydroxide (TMAH) aqueoussolution, thereby forming a photoresist pattern on the substrate.

The photoresist composition serving as a material from which photoresistpatterns are formed is not limited in any particular way and any commonphotoresist compositions may be employed including those for exposure toi- or g-lines, those for exposure with an excimer laser (e.g. KrF, ArFor F₂) and those for exposure to EB (electron beams).

[a.] Over-coating Agent Application Step

An over-coating agent is applied to cover entirely the said substratehaving photoresist patterns (mask patterns) thereon. After applying theover-coating agent, the substrate may optionally be pre-baked at atemperature of 80-100° C. for 30-90 seconds.

The over-coating agent may be applied by any methods commonly employedin the conventional heat flow process. Specifically, an aqueous solutionof the over-coating agent for forming fine patterns is applied to thesubstrate by any known application methods including bar coating, rollcoating and whirl coating with a spinner.

The over-coating agent employed in the invention is to cover entirelythe substrate having photoresist patterns (mask patterns) thereon,including patterns typified by hole patterns or trench patterns, each ofthese patterns are defined by spacing between adjacent photoresistpatterns (mask patterns). Upon heating, the applied film of over-coatingagent shrinks to increase the width of each of the photoresist patterns,thereby narrowing or lessening adjacent hole patterns or trench patternsas defined by spacing between the photoresist patterns and, thereafter,the applied film is removed substantially completely to form or definefine featured patterns.

The phrase “removing the applied film substantially completely” as usedherein means that after lessening the spacing between adjacentphotoresist patterns by the heat shrinking action of the appliedover-coating agent, said film is removed in such a way that nosignificant thickness of the over-coating agent will remain at theinterface with the photoresist patterns. Therefore, the presentinvention does not include methods in which a certain thickness of theover-coating agent is left intact near the interface with thephotoresist pattern so that the feature size of the pattern is reducedby an amount corresponding to the residual thickness of the over-coatingagent.

In the present invention, the over-coating agent is preferably employedthat contains a water-soluble polymer.

The water-soluble polymer may be any polymer that can dissolve in waterat room temperature and various types may be employed without particularlimitation; preferred examples include acrylic polymers, vinyl polymers,cellulosic derivatives, alkylene glycol polymers, urea polymers,melamine polymers, epoxy polymers and amide polymers.

Exemplary acrylic polymers include polymers and copolymers havingmonomeric components, such as acrylic acid, methyl acrylate, methacrylicacid, methyl methacrylate, N,N-dimethylacrylamide,N,N-dimethylaminopropylmethacrylamide,N,N-dimethylaminopropylacrylamide, N-methylacrylamide, diacetoneacrylamide, N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethylmethacrylate, N,N-dimethylaminoethyl acrylate, acryloylmorpholine, etc.

Exemplary vinyl polymers include polymers and copolymers havingmonomeric components, such as N-vinylpyrrolidone, vinyl imidazolidinone,vinyl acetate, etc.

Exemplary cellulosic derivatives include hydroxypropylmethyl cellulosephthalate, hydroxypropylmethyl cellulose acetate phthalate,hydroxypropylmethyl cellulose hexahydrophthalate, hydroxypropylmethylcellulose acetate succinate, hydroxypropylmethyl cellulose,hydroxypropyl cellulose, hydroxyethyl cellulose, cellulose acetatehexahydrophthalate, carboxymethyl cellulose, ethyl cellulose,methylcellulose, etc.

Exemplary alkylene glycol polymers include addition polymers andcopolymers of ethylene glycol, propylene glycol, etc.

Exemplary urea polymers include those having methyllolurea,dimethylolurea, ethyleneurea, etc. as components.

Exemplary melamine polymers include those having methoxymethylatedmelamine, methoxymethylated isobutoxymethylated melamine,methoxyethylated melamine, etc. as components.

Among epoxy polymers and amide polymers, those which are water-solublemay also be employed.

It is particularly preferred to employ at least one member selected fromthe group consisting of alkylene glycol polymers, cellulosicderivatives, vinyl polymers and acrylic polymers. Acrylic polymers aremost preferred since they provide ease in pH adjustment. Copolymerscomprising acrylic polymers and water-soluble polymers other thanacrylic polymers are also preferred since during heat treatment, theefficiency of shrinking the spacing between the adjacent photoresistpatterns (mask patterns) can be increased while maintaining the shape ofthe photoresist pattern. The water-soluble polymers can be employedeither singly or in combination.

When water-soluble polymers are used as copolymers, the proportions ofthe components are not limited to any particular values. However, ifstability over time is important, the proportion of the acrylic polymeris preferably adjusted to be larger than those of other buildingpolymers. Other than by using excessive amounts of the acrylic polymer,better stability over time can also be obtained by adding acidiccompounds such as p-toluenesulfonic acid and dodecylbenzenesulfonicacid.

The over-coating agent for forming fine patterns may additionallycontain water-soluble amines. Preferred ones include amines having pKa(acid dissociation constant) values of 7.5-13 in aqueous solution at 25°C. in view of the prevention of the generation of impurities and pHadjustment. Specific examples include the following: alkanolamines, suchas monoethanolamine, diethanolamine, triethanolamine,2-(2-aminoethoxy)ethanol, N,N-dimethylethanolamine,N,N-diethylethanolamine, N,N-dibutylethanolamine, N-methylethanolamine,N-ethylethanolamine, N-butylethanolamine, N-methyldiethanolamine,monoisopropanolamine, diisopropanolamine and triisopropanolamine;polyalkylenepolyamines, such as diethylenetriamine,triethylenetetramine, propylenediamine, N,N-diethylethylenediamine,1,4-butanediamine, N-ethylethylenediamine, 1,2-propanediamine,1,3-propanediamine and 1,6-hexanediamine; aliphatic amines, such astriethylamine, 2-ethyl-hexylamine, dioctylamine, tributylamine,tripropylamine, triallylamine, heptylamine and cyclohexylamine; aromaticamines, such as benzylamine and diphenylamine; and cyclic amines, suchas piperazine, N-methyl-piperazine and hydroxyethylpiperazine. Preferredwater-soluble amines are those having boiling points of 140° C. (760mmHg) and above, as exemplified by monoethanolamine and triethanolamine.

If the water-soluble amine is to be added, it is preferably incorporatedin an amount of about 0.1-30 mass %, more preferably about 2-15 mass %,of the over-coating agent (in terms of solids content). If thewater-soluble amine is incorporated in an amount of less than 0.1 mass%, the coating fluid may deteriorate over time. If the water-solubleamine is incorporated in an amount exceeding 30 mass %, the photoresistpattern being formed may deteriorate in shape.

The over-coating agent for forming fine patterns is adjusted to have pHvalues of 2-3 by the addition of the water-soluble amine. There may becases where the over-coating agent for forming fine patterns is appliedto the substrate having metallic layers easily corroded by an acid, thepH values may be adjusted to 3-5.

For such purposes as reducing the dimensions of patterns and controllingthe occurrence of defects, the over-coating agent for forming finepatterns may further optionally contain non-amine based, water-solubleorganic solvents.

As such non-amine based, water-soluble organic solvents, any non-aminebased organic solvents that can mix with water may be employed and theymay be exemplified by the following: sulfoxides, such as dimethylsulfoxide; sulfones, such as dimethylsulfone, diethylsulfone,bis(2-hydroxyethyl)sulfone and tetramethylenesulfone; amides, such asN,N-dimethylformamide, N-methylformamide, N,N-dimethylacetamide,N-methylacetamine and N,N-diethylacetamide; lactams, such asN-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-propyl-2-pyrrolidone,N-hydroxymethyl-2-pyrrolidone and N-hydroxyethyl-2-pyrrolidone;imidazolidinones, such as 1,3-dimethyl-2-imidazolidinone,1,3-diethyl-2-imidazolidinone and 1,3-diisopropyl-2-imidazolidinone; andpolyhydric alcohols and derivatives thereof, such as ethylene glycol,ethylene glycol monomethyl ether, ethylene glycol monoethyl ether,ethylene glycol monobuthyl ether, ethylene glycol monomethyl etheracetate, ethylene glycol monoethyl ether acetate, diethylene glycol,diethylene glycol monomethyl ether, diethylene glycol monoethyl ether,diethylene glycol monobuthyl ether, propylene glycol, propylene glycolmonomethyl ether, glycerol, 1,2-butylene glycol, 1,3-butylene glycol and2,3-butylene glycol. Among those mentioned above, polyhydric alcoholsand their derivatives are preferred for the purposes of reducing thedimensions of patterns and controlling the occurrence of defects andglycerol is particularly preferred. The non-amine based, water-solubleorganic solvents may be used either singly or in combination.

If the non-amine based, water-soluble organic solvent is to be added, itis preferably incorporated in an amount of about 0.1-30 mass %, morepreferably about 0.5-15 mass %, of the water-soluble polymer. If thenon-amine based, water-soluble organic solvent is incorporated in anamount of less than 0.1 mass %, its defect reducing effect tends todecrease. Beyond 30 mass %, a mixing layer is liable to form at theinterface with the photoresist pattern.

In addition, the over-coating agent may optionally contain a surfactantfor attaining special effects such as coating uniformity and wafer'sin-plane uniformity.

The surfactant is preferably employed that, when added to thewater-soluble polymer, exhibits certain characteristics such as highsolubility, non-formation of a suspension and miscibility with thepolymer component. By using surfactants that satisfy thesecharacteristics, the occurrence of defects can be effectively controlledthat is considered to be pertinent to microforming upon coating theover-coating agent.

From the points above, surfactants in the invention are preferablyemployed at least the one selected among N-alkylpyrrolidones, quaternaryammonium salts and phosphate esters of polyoxyethylene.

N-alkylpyrrolidones as surfactant are preferably represented by thefollowing general formula (I):

where R₁ is an alkyl group having at least 6 carbon atoms.

Specific examples of N-alkylpyrrolidones as surfactant includeN-hexyl-2-pyrrolidone, N-heptyl-2-pyrrolidone, N-octyl-2-pyrrolidone,N-nonyl-2-pyrrolidone, N-decyl-2-pyrrolidone, N-undecyl-2-pyrrolidone,N-dodecyl-2-pyrrolidone, N-tridecyl-2-pyrrolidone,N-tetradecyl-2-pyrrolidone, N-pentadecyl-2-pyrrolidone,N-hexadecyl-2-pyrrolidone, N-heptadecyl-2-pyrrolidone andN-octadecyl-2-pyrrolidone. Among these, N-octyl-2-pyrrolidone(“SURFADONE LP 100” of ISP Inc.) is preferably used.

Quaternary ammonium salts as surfactant are preferably represented bythe following general formula (II):

where R₂, R₃, R₄ and R₅ are each independently an alkyl group or ahydroxyalkyl group (provided that at least one of them is an alkyl orhydroxyalkyl group having not less than 6 carbon atoms); X⁻ is ahydroxide ion or a halogenide ion.

Specific examples of quaternary ammonium salts as surfactant includedodecyltrimethylammonium hydroxide, tridecyltrimethylammonium hydroxide,tetradecyltrimethylammonium hydroxide, pentadecyltrimethylammoniumhydroxide, hexadecyltrimethylammonium hydroxide,heptadecyltrimethylammonium hydroxide and octadecyltrimethylammoniumhydroxide. Among these, hexadecyltrimethylammonium hydroxide ispreferably used.

Phosphate esters of polyoxyethylene are preferably represented by thefollowing general formula (III):

where R₆ is an alkyl or alkylaryl group having 1-10 carbon atoms; R₇ isa hydrogen atom or (CH₂CH₂O)R₆ (where R₆ is as defined above); n is aninteger of 1-20.

To mention specific examples, phosphate esters of polyoxyethylene thatcan be used as surfactants are commercially available under trade names“PLYSURF A212E” and “PLYSURF A210G” from Dai-ichi Kogyo Seiyaku Co.,Ltd. If the surfactant is to be added, it is preferably incorporated inan amount of about 0.1-10 mass %, more preferably about 0.2-2 mass %, ofthe over-coating agent (in terms of solids content). By adopting theamount as described above ranges, it may effectively prevent thevariations in the percent shrinkage of patterns, potentially dependingon the wafer's in-plane uniformity which is caused by the deteriorationof coating property, and also prevent the occurrence of defects that areconsidered to have cause-and-effect relations with microfoaming on theapplied film that generates as the coating conditions are worsened.

The over-coating agent of the invention for forming fine patterns ispreferably used as an aqueous solution at a concentration of 3-50 mass%, more preferably at 5-30 mass %. If the concentration of the aqueoussolution is less than 3 mass %, poor coverage of the substrate mayresult. If the concentration of the aqueous solution exceeds 50 mass %,there is no appreciable improvement in the intended effect thatjustifies the increased concentration and the solution cannot be handledefficiently.

As already mentioned, the over-coating agent in the invention forforming fine patterns is usually employed as an aqueous solution usingwater as the solvent. A mixed solvent system comprising water and analcoholic solvent may also be employed. Exemplary alcoholic solventsinclude methyl alcohol, ethyl alcohol, propyl alcohol, isopropylalcohol, glycerol, ethylene glycol, propylene glycol, 1,2-butyleneglycol, 1,3-buthylene glycol and 2,3-butylene glycol, etc. Thesealcoholic solvents are mixed with water in amounts not exceeding about30 mass %.

[b.] Heat Treatment (Thermal Shrinkage) Step

In the next step, heat treatment is performed to cause thermal shrinkageof the film of the over-coating agent. Under the resulting force ofthermal shrinkage of the film, the dimensions of the photoresist patternin contact with the film will increase by an amount equivalent to thethermal shrinkage of the film and, as the result, the photoresistpattern widens and accordingly the spacing between adjacent photoresistpatterns lessens. The spacing between adjacent photoresist patternsdetermines the diameter or width of the pattern elements to be finallyobtained, so the decrease in the spacing between adjacent photoresistpatterns contributes to reducing the diameter of each element of a holepattern or the width of each element of a trench pattern, eventuallyleading to the definition of a pattern with smaller feature sizes.

The heating temperature is not limited to any particular value as longas it is high enough to cause thermal shrinkage of the film of theover-coating agent and form or define a fine pattern. Heating ispreferably done at a temperature that will not cause thermal fluidizingof the photoresist pattern. The temperature that will not cause thermalfluidizing of the photoresist pattern is such a temperature that when asubstrate on which the photoresist pattern has been formed but no filmof the over-coating agent has been formed is heated, the photoresistpattern will not experience any dimensional changes. Performing a heattreatment under such temperature conditions is very effective forvarious reasons, e.g. a fine-line pattern of good profile can be formedmore efficiently and the duty ratio in the plane of a wafer, or thedependency on the spacing between photoresist patterns in the plane of awafer, can be reduced. Considering the softening points of a variety ofphotoresist compositions employed in current photolithographictechniques, the preferred heat treatment is usually performed within atemperature range of about 80-160° C. for 30-90 seconds, provided thatthe temperature is not high enough to cause thermal fluidizing of thephotoresist.

The thickness of the film of the over-coating agent for the formation offine-line patterns is preferably just comparable to the height of thephotoresist pattern or high enough to cover it.

[c.] Over-coating Agent Removal Step

In the subsequent step, the remaining film of the over-coating agent onthe patterns is removed substantially completely by bringing thuslytreated substrate into contact with a remover solution for over 60seconds, and preferably 70 seconds or over. By adjusting the contacttime of the substrate with the remover solution to be over 60 seconds,it is extremely effective in reducing the occurrence of defects on thesubstrate without lowering throughput. If the contact time is 60 secondor less, defects occur on the substrate and the yields be lowered. Theupper time of the contact is not specifically limited, however, it ispreferred 300 seconds or less in view of the reduction of the occurrenceof defects and the improvement of throughput, etc. The method of thecontact may be employed such as a puddle method, a dipping method, ashower method, a spray method, etc., but not limited thereto.

The remover solution is suitably used a water-based solvent, and morepreferably pure water. Prior to the removal step, rinsing may optionallybe performed with an aqueous solution of alkali (e.g.tetramethylammonium hydroxide (TMAH) or choline). The over-coating agentin the present invention is easy to remove by washing with water and itcan be completely removed from the substrate and the photoresistpattern. The present invention can effectively reduce the occurrence ofdefects entirely. Specifically, among varieties of defects, the presentinvention is extremely effective in reducing the occurrence of thedefects that are filled in the portions of holes and spacing areas.

As a result, each pattern on the substrate has a smaller feature sizebecause each pattern is defined by the narrowed spacing between theadjacent widened photoresist patterns.

The fine-line pattern thus formed using the over-coating agent of thepresent invention has a pattern size smaller than the resolution limitattainable by the conventional methods. In addition, it has a goodenough profile and physical properties that can fully satisfy thecharacteristics required of semiconductor devices.

Steps [a.]-[c.] may be repeated several times. By repeating steps[a.]-[c.] several times, the photoresist trace patterns (mask patterns)can be progressively widened. Furthermore, the use of the over-coatingagent for forming fine patterns containing a water-soluble polymerallows the over-coating agent be completely removed with water everytime in repeating the removal step plural times. Therefore, the presentinvention offers the advantage that even in the case of using asubstrate having thick-film photoresist patterns, fine-line patterns ofgood profile can be formed on the substrate without causing patterndistortion or deformation.

The technical field of the present invention is the semiconductorindustry, etc., but it is not limited thereto.

EXAMPLES

The following examples are provided for further illustrating the presentinvention but are in no way to be taken as limiting. Unless otherwisenoted, all amounts of ingredients are expressed in mass %.

Example 1

A copolymer including polyacrylate (PAA) and polyvinylpyrrolidone (PVP)[2 g; PAA/PVP=2:1 (polymerization ratio)], triethanolamine (0.18 g) anda polyoxyethyelene phosphate ester surfactant (0.02 g; “PLYSURF A210G”,product of Dai-ichi Kogyo Seiyaku Co, Ltd.) were dissolved in water (52g) to prepare an over-coating agent.

A substrate (8-inch diameter) was whirl coated with a positive-actingphotoresist TDUR-P036PM (product of Tokyo Ohka Kogyo Co., Ltd.) andbaked at 80° C. for 90 seconds to form a photoresist layer in athickness of 0.48 μm.

The photoresist layer was exposed with an exposure unit (CanonEPA-3000EX3, product of Canon Inc.), subjected to heat treatment at 120°C. for 90 seconds and developed with an aqueous solution of 2.38 mass %TMAH (tetramethylammonium hydroxide) to form photoresist patterns whichdefined hole patterns with an each diameter of 178.9 nm (i.e., thespacing between the photoresist patterns, or the initial hole dimension,was 178.9 nm).

The previously prepared over-coating agent was applied onto thesubstrate including hole patterns and subjected to heat treatment at116° C. for 60 seconds, thereby reducing the each size of the holepatterns.

Subsequently, the substrate, while being kept whirling at 1500 rpm, wasbrought into contact with pure water by dropping it on the substrate for120 seconds to remove the over-coating agent. The each diameter of thehole patterns was reduced to 150.8 nm. The state of defects on thesubstrate was observed with KLA (product of KLA Tencor), however, fewdefects were occurred on the entire substrate.

Example 2

The same procedure as described in Example 1 was repeated, except thatthe substrate was brought into contact with pure water by dropping it onthe substrate for 90 seconds. Each diameter of the hole patterns wasnarrowed to 158.3 nm, and few defects were occurred on the entiresubstrate.

Comparative Example 1

The same procedure as described in Example 1 was repeated, except thatthe substrate was brought into contact with pure water by dropping it onthe substrate for 60 seconds. Each diameter of the hole patterns wasnarrowed to 158.8 nm. However, the observation with KLA revealed theoccurrence of defects on the order of 10-20 in numbers on the substrate.

As described above in detail, the present invention provide a method forforming fine patterns, by which advantages obtained of reducing theoccurrence of defects and improving throughput.

1. A method of forming fine patterns comprising: covering a substratehaving photoresist patterns with an over-coating agent for forming finepatterns, applying heat treatment, wherein the heat treatment isperformed at a temperature that does not cause thermal fluidizing of thephotoresist patterns on the substrate, to cause thermal shrinkage of theover-coating agent so that the spacing between adjacent photoresistpatterns is lessened by the resulting thermal shrinking action, andremoving the over-coating agent substantially completely by way ofbringing thusly treated substrate into contact with a remover solutionfor over 60 seconds.
 2. The method of forming fine patterns according toclaim 1, wherein the over-coating agent contains a water-solublepolymer.
 3. The method of forming fine patterns according to claim 2,wherein the water-soluble polymer is at least one member selected fromthe group consisting of alkylene glycolic polymers, cellulosicderivatives, vinyl polymers, acrylic polymers, urea polymers, epoxypolymers, melamine polymers and amide polymers.
 4. The method of formingfine patterns according to claim 1, wherein the over-coating agent is anaqueous solution having a solids content of 3-50 mass %.
 5. The methodaccording to claim 2 wherein the over-coating agent further contains awater-soluble amine.
 6. The method according to claim 1 wherein theover-coating agent contains a non-amine based, water-soluble organicsolvent.
 7. The method according to claim 2 wherein a water solublesurfactant is added to the water soluble polymer.